Emotion Regulation (ER) is the ability to modulate the expression of emotion and accompanying arousal states. Deficits in this capacity severely compromise one's capacities to participate in social interactions and to adapt to one's environment. Over time, significant difficulties are likely to lead to psychopathology. The foundation of ER capabilities is established during infancy as Infants first face the task of ER. Therefore, delays or deficits during this time may foreshadow maladaptive or ineffective ER processes in childhood and adulthood. Previous research has described ER behaviors used by infants. However, significantly fewer studies have examined developmental changes in ER behaviors and the processes by which they are controlled. These issues are central to a comprehensive theory of ER development and to understanding how competent versus incompetent forms of ER may emerge. The proposed cross-sectional study will examine age-related changes in: 1) the specific ER behaviors used by infants and the impact these behaviors have upon distress; 2) the range and type of ER behaviors employed by infants; 3) ERA control processes. This study will provide the basis for a more comprehensive study that will explore the evolution of individual differences in ER competence. The proposed study is cross-sectional in design and will include 3 groups of healthy, full-term infants: 4-, 9-, 12-month-old infants. Each group will include 30 infants. Infants will be presented with a series of stimuli that typically evoke negative affect during the first year of life: 1) approach of a novel adult; 2) intrusive game with a novel adult (i.e. pattycake); 3) hat placement; 4) brief arm restraint. These situations will be used to elicit negative affect and ER behaviors within each age-group. Infants' affect expressions and ER behaviors will be coded in 1-second intervals as stimuli are presented. Sequential time analyses will be used to explore the links between specific ER behaviors and changes in the intensity of negative affect within and across the different age groups. Additional analyses will explore group differences in: 1) the range of ER behaviors displayed; 2) the type of ER behaviors displayed; 3) relative usage of individual ER behaviors. A fifth set of sequential time analyses will examine the extent to which changes in affect intensity are related to the initiation, maintenance, switching and termination of ER behaviors. This set of analyses will explore the flexibility of ER control processes within and across the different age groups.